Circuit arrangement for polarity reversal of signals from a signal source

ABSTRACT

A polarity reversal arrangement provided with two seriesarranged electronic switching elements, for example, for use in pulse code modulation. freedom In order to satisfy the strict requirements of polarity reversal at the instants of an alternation of polarity of the signals from a signal source and the requirement of freedom from distortion, the polarity reversal arrangement is provided with a bridge composed of resistors wherein the signal source is connected to one end of a diagonal branch of the bridge and wherein the input circuit of an amplifier reversing the polarity of the input signal is connected to the other end of this diagonal branch and wherein the series arrangement of the two electronic switching elements is included between the ends of the other diagonal branch, the junction of the electronic switching elements being connected to the output circuit of the amplifier, while the output signals of the polarity reversal arrangement are derived from one end of the last-mentioned diagonal branch of the bridge.

United States Patent REVERSAL 0F SIGNALS FROM A SIGNAL SOURCE 7 Claims,2 Drawing Figs.

3,130,325 4/1964 Rubin et a1. 307/229 3,196,291 7/1965 Woodward, .lr.307/229 3,311,835 3/1967 Richman 328/26 X 3,480,794 11/1969 Richman307/261 X 3,509,372 4/1970 Bicking 307/236 Primary Examiner-Stanley T.Krawczewicz A!l0rneyFrank R. Trifari ABSTRACT: A polarity reversalarrangement provided with two series-arranged electronic switchingelements, for example, for use in pulse code modulation. freedom Inorder to satisfy the strict requirements of polarity reversal at theinstants ofan alternation of polarity of the signals from a signalsource and the requirement of freedom from distortion, the polarityreversal arrangement is provided with a bridge composed of resistorswherein the signal source is connected [52] US. Cl 307/262, to one endofa diagonal branch of the bridge and wherein the 307/229, 307/236,307/261, 321/8, 328/26, input circuit of an amplifier reversing thepolarity of the input 328/140 signal is connected to the other end ofthis diagonal branch [51 lnt. Cl l-l03k 1/12, and wherein the seriesarrangement of the two electronic H02m 7/00 switching elements isincluded between the ends of the other [50] Field of Search 307/229,diagonal branch, the junction of the electronic switching ele- 236, 261,262; 328/26, 55, 57, 118, 140, 142, 143; ments being connected to theoutput circuit of the amplifier, 321/8 while the output signals of thepolarity reversal arrangement are derived from one end of thelast-mentioned diagonal References (med branch of the bridge.

UNITED STATES PATENTS 3,112,449 1 H1963 Miller 328/26 AMPL/F/ER PULSECODE MODULATOR 19 C I i 7 l7 8 A5 L I ;Z 10 I 7L I d I f i l 5 12 21 iAMPL /F/R 22 CIRCUIT ARRANGEMENT F OR POLARIT Y REVERSAL F SIGNALS F ROMA SIGNAL SOURCE The invention relates to a circuit arrangement forpolarity reversal of signals from a signal source, which circuitarrangement is provided with two series-arranged electronic switchingelements. Such circuit arrangements for polarity reversal are used interalia in pulse code modulation transmission devices for generatingrectified speech signals by means of polarity reversal, in particularthe rectified speech signals thus obtained are applied to a pulse codemodulator for generating the pulse code groups to be transmitted whichare transferred to the receiver together with a polarity pulsecharacterizing the polarity of the speech signals to be transmitted.

Special care is to be bestowed on the construction of such circuitarrangements for polarity reversal. In fact, on the one hand it shouldbe ensured that the polarity reversal takes place exactly at theinstants of change of polarity of the speech signals, since as has beenfound from extensive investigations already small deviations from theseinstants for polarity reversal are disturbingly noticeable in thereproduction of the transmitted speech signals. On the other handdistortions and influences by disturbing effects such as, for example,temperature effects, direct current drift phenomena etc. are to beavoided.

It is an object of the present invention to provide a circuitarrangement of the type described in the preamble which is simple andconvenient in construction, and in which the above-mentionedrequirements for polarity reversal are satisfied, while this circuitarrangement is furthermore distinguished by its wide possibilities ofuse.

According to the invention the circuit arrangement for polarity reversalis provided with a bridge composed of resistors, the signal sourcebeingconnected to one end of a diagonal branch of the bridge and the inputcircuit of an amplifier which reverses the polarity of the input signalbeing connected to the other end of this diagonal branch, the seriesarrangement of the two electronic switching elements being includedbetween the ends of the other diagonal branch, the junction of theelectronic switching elements being connected to the output circuit ofthe amplifier while the output signals of the polarity reversalarrangement are derived from one end of the last-mentioned diagonalbranch of the bridge.

In order that the invention may be readily carried into effect, a fewembodiments thereof will now be described in detail, by way of example,with reference to the accompanying diagrammatic drawing, in which FIG. Ishows a circuit arrangement for polarity reversal according to theinvention, while FIG. 2 shows a modification of the circuit FIG. 1.

The circuit arrangement shown in FIG. I for polarity reversal accordingto the invention is intended for generating rectified signals by meansof polarity reversal in the band of 0.3--l0 kHz., which signalsoriginate from a signal source including output terminals 2, 3 and aninternal resistor 4, the output terminal 2 of said source beingconnected to a point of fixed potential, for example, earth potential,and the other output terminal 3 of the source being connected to theinput circuit of the circuit arrangement which for the purpose ofpolarity reversal of the signals from the signal source 1 is providedwith two series-arranged electronic switching elements 5, 6 in the formof diodes. The output signals of the circuit arrangement are applied forhandling in a user 7, for example, a pulse code modulator to anamplifier 8 having a high input resistance.

In order to satisfy the strict requirements of polarity reversal at theinstants of an alternation of polarity of the signals from the signalsource 1 and the requirements of freedom from distortion, the polarityreversal arrangement according to the invention is provided with abridge composed of resistors 9, 10, 11, 12, the signal source 1 beingconnected to one end 13 of a diagonal branch of the bridge and the inputcircuit of an amplifier I5, which reverses the polarity of the inputsignal,

arrangement of being connected to the other end 14 of this diagonalbranch the series arrangement of the two diodes 5, 6, being includedbetween the ends 16, 17 of the other diagonal branch, the junction ofthe diodes 5, 6 being connected to the output circuit of the amplifier15, while the output signals of the polarity reversal arrangement arederived from the end 17 of the lastmentioned diagonal branch of thebridge. In the embodiment shown the amplitude of each bridge resistor 9,10, ll, 12 is equal to R with, for example, R=lkfl and the amplifier 15has a very high input resistance and a high amplification factor, forexample, u=l0,000 while the amplifier 15 is adjusted in such a mannerthat in the absence of signals from the signal source I the potential ofthe input circuit and output circuit is equal to the fixed potential ofthe output terminal 2 of the signal source 1.

Dependent on the speech signal originating from the signal source 1having a positive or negative polarity, the diode 6 will be conductingand the diode 5 will be blocked or conversely the diode 5 will beconducting and the diode 6 will be blocked, the amplifier 15 beingnegatively fed back either across the resistor II or across the resistor12 through the then conducting diode. In case of an alternation ofpolarity a reversal of the negative feedback circuits of the amplifier15 takes place, which negative feedback circuits are formed .by diode 6and resistor 11 and diode 5 and resistor 12, respectively, and as aresult of this reversal of the negative feedback circuits by means ofpolarity reversal a rectification of the signal originating from thesignal source 1 takes place, which is diagrammatically shown in theFigure by the time diagram I8. The rectified signal from the signalsource 1 occurs at the diagonal points l6, 17 of the bridge, in theembodiment shown, for example, the rectified signal is derived fromdiagonal point 17 for further handling in the user 7 by means of theamplifier 8 having the high input resistance.

Starting from the condition in which there is no signal from the signalsource 1 available, the behavior of the polarity reversal arrangement incase of a positive and a negative signal voltage will be examined so asto explain the operation.

If, starting from this condition in which the diagonal point 13 and theinput circuit and the output circuit of the amplifier 15 are thusconnected to earth potential, at positive signal voltage from the signalsource 1 is applied to the diagonal point 13 of the bridge, then apositive signal voltage will likewise occur at the input circuit of theamplifier l3 and a negative signal voltage will occur at the output ofthe amplifier 15, which already at an extremely small input signal opensthe diode 6 due to the high amplification factor of the amplifier 15, sothat the amplifier 15 will be negatively fed back through the resistor11 and as a result of this negative feedback the amplifier 15 shows thetendency to counteract any variation in its input voltage, that is tosay, the diagonal point 14 is substantially maintained at earthpotential. When the signal voltage at the diagonal point 13 is 1 volt, avoltage of approximately 10 volts occurs, for example, at the diagonalpoint 14 connected to the input circuit of the amplifier 15.

The course of the current in the bridge in case of a positive signalvoltage is shown for the purpose of illustration in the Figure by solidline arrows, during which no signal current is assumed by the amplifiers8 and 15 due to their high input resistances so that no distortions arecaused thereby. If the diagonal point 13 connected to the signal sourceI has a positive signal voltage E, then a voltage of +(R/2R)E=-+-E/2 or(R/2AY)E='E/2 will occur at the diagonal point 17, 16, respectively,under the circumstances mentioned at which the diagonal point 14 issubstantially connected to earth potential and each resistor 9, 10, l1,I2 is equal to R. When shown diagrammatically, voltages then occur atthe diagonal points l7, 16 which voltages have a variation as is shownby the solid-line curves in the time diagrams 19, 20.

Conversely, the diode 5 will be opened when the signal voltage at thediagonal point 13 connected to the signal source I is negative and theamplifier 15 will be negatively fed back through the resistor 12, thediagonal point 14 connected to the input circuit of the amplifier 15being maintained substantially at earth potential due to the negativefeedback likewise as is the case for a positive signal voltage. Thecourse of the current in the bridge is shown by the broken line arrowsand voltages of -(R/2R)E -E/2 and +(R /2R)E=+E /2 will then occur at thediagonal points 17, 16, respectively, when the signal voltage E at thediagonal point 13 connected to the signal source 1 is negative, whilethe variation of these voltages is shown by the broken line curves inthe time diagrams I9, 20. As may be apparent from these time diagrams19, 20, the rectified signals from the signal source 1 occur in abalanced form at the diagonal points l7, 16, the rectified signals atthe diagonal point 17 in the embodiment shown being utilized for furtherhandling in the user 7.

The polarity reversal in the circuit arrangement shown occurs exactly atthe instant of the alternations of polarity of the signals to betransmitted so that due to the high amplification factor of theamplifier l5 and the negative feedback effect disturbing phenomena areprevented such as, for example, ageing phenomena, distortions in theamplifier l5 and the diodes S, 6, but also temperature effects anddirect current drift phenomena since the negative feedback circuits ofthe amplifier also function as direct voltage negative feedbackcircuits.

If the signal source 1 is formed by a current source these directcurrent drift phenomena even exert no influence at all on the polarityreversal since due to the high internal resistance of the current source1 the diagonal point 13 connected to the current source will assume thesame potential as that of the diagonal point 14 connected to the inputof the amplifier 15, so that consequently a voltage difference betweenthese diagonal points 13, 14 will not occur in the absence of a speechsignal. If the signal source 1 is formed by a voltage source, thealready slight influence of the direct current drift of the amplifier 15can still further be reduced without disturbing the course of thecurrent in the bridge by using an additional direct voltage negativefeedback circuit in the amplifier 15 especially constructed for thispurpose in the manner as is shown in the Figure.

Particularly, the amplifier 15 is provided with an input amplifier stage21 employing a field effect transistor (FET), the source electrode beingconnected to the input of the subsequent amplifier stage 22 whilst theFET 21 which, as is known, has a very high input impedance is fed by acurrent source incorporated in the source electrode circuit in the formof a difference amplifier 23 provided with transistors 24, 25 having acommon emitter resistor 26. To compensate for the direct current driftof the amplifier, the base electrode of the transistor 24 is connectedto earth potential through resistor 27, and the base electrode of thetransistor 25 is connected to the output circuit of the amplifier 15through a low-pass filter which does not pass signal frequencies and iscomposed of series resistors 28, 29 and shunt capacitors 30, 31.

In this case the direct current drift of the amplifier 15 is compensatedfor in the manner of a direct voltage negative feedback. If a directcurrent drift occurs, for example, at the output of the amplifier 15,the collector current of the transistor 24 and hence the current throughthe FET 21 will consequently start to vary low-pass filter 28-31 and thetransistor 25 as a result of which also the voltage between the controlelectrode and the source electrode of the FET 21 will vary which voltagevariation will bring about the direct current drift compensation of theamplifier 15 without a direct current being introduced into the controlelectrode circuit, or in other words, without the course of the currentin the bridge 9-12 being disturbed.

The following data are mentioned below for a polarity reversalarrangement which was extensively tested in practice.

l3.9,l0,ll,l2: lKQ diodes 5, 6.- BAX l3. Resistors 28, 29: 5 KOCapacitors 30. 31: 10 pl.

Deviation in the polarity reversal arrangement: 0.! mv.

distortion level: smaller than 60 db. Transistors 24. 25: BCY H7.

Resistor 26: 3 K1] Resistor 27: [0 K0 FET 21; BFW I I.

In addition to the advantages of optimum results and simplicity inconstruction, the polarity reversal arrangement provides the greatadvantage of a great frequency independence, particularly the polarityreversal arrangement shown can be used for the lowest signal frequenciesas occur, for example, in video signals.

In addition, the arrangement described is distinguished by its widepossibilities of use. The rectified output signals may be derived, forexample, both in a balanced form and in single phase, and thepossibility of capacitive coupling of the signal source 1 and the outputamplifier 8 is provided without having to use extreme capacitances dueto the possibility of using a. signal source 1 having a high internalresistance and an output amplifier 8 having a high input resistance.

If desired, there is the possibility of a transformer coupling of thesignal source 1 to the bridge in which case the transformer ispreferably incorporated between the diagonal points 13, 14.

In the circuit arrangement described so far the polarity reversal takesplace by the signals from the signal source 1 itself while usingswitching elements in the form of diodes 5, 6, whereas the polarityreversal in the circuit arrangement of FIG. 2 is effected by separatecontrol signals, for example, for use of a circuit arrangement for pulsecode demodulation shown in FIG. 2. The circuit arrangement of FIG. 2 isadapted for demodulation of pulse groups transmitted with the aid ofpulse code modulation, wherein the first pulse wave always functions asa polarity pulse and the other pulses in a pulse group characterize theamplitude value of the rectified speech signal. Elements correspondingto those in FlG. 1 have the same reference numerals in FIG. 2.

ln the circuit arrangement for pulse code demodulation shown in FlG. 2the pulse groups received through line 32 are applied to a pulse codedemodulator 35 after suppressing the polarity pulse in an inhibitor gate34; samplings occurring at the output circuit of the pulse codedemodulator 35 which samplings have the variation shown in the timediagram 37 upon transmission of, for example, the signal as isillustrated in the time diagram 19 of FIG, 1. Both the inhibitor gate 34and the pulse code demodulator 35 are controlled by a local pulsegenerator 33 which is accurately synchronized at the frequency of thereceived pulse groups, for example, by means of cotransmittedsynchronizing pulses.

An AND-gate 38 controlled by the local pulse generator 33 is alsoconnected to the line 32 for selection of the polarity pulses in thepulse groups, which selection gate 38 is succeeded by an inverter 39connected to the local pulse generator 33 and has two output lines 40,41 for the control of a bistable trigger 42 which is likewise providedwith two control lines 43, 44 for the electronic switching elements 45,46 of the polarity reversal arrangement, each electronic switchingelement 45, 46 being provided with a control electrode and, for example,formed by field effect transistors. in the arrangement shown thepolarity pulses selected in the AND-gate 38 and consisting of l pulsesat a position polarity and 0 pulses at a negative polarity are appliedto the inverter 39 which applies a pulse to output line 40 in case of a1 pulse as a polarity pulse and which applies a pulse to output line 41in case of a 0 pulse as a polarity pulse, the bistable trigger 42assuming one stable state as a result of the pulses of the output line40 and assuming the other stable state as a result of the pulses of theoutput line 41. The control signals for the electronic switchingelements 45, 46 are derived in this manner from the output circuits 43,44 of the bistable trigger 42, which switching elements are consequentlybrought, for example, from their blocked condition to the conductingcondition.

In fact, dependent on the polarity pulse being formed by a 1 pulse of a0 pulse, the bistable trigger 42 supplies either a control signal forthe electronic switching element 46 through control line 43, or acontrol signal for the electronic switching element 45 through controlline 44, the polarity reversal being effected in the manner as alreadydescribed with reference to FIG. 1 due to the mentioned control of theelectronic switching elements 45, 46. If, for example, a 1 pulse occursas a polarity pulse indicating a signal of positive polarity to betransmitted, then the electronic switching element 46 is conducting andthe sampling, which is then present at the output of the pulse codedemodulator 35, occurs with positive polarity at the diagonal point 17and with negative polarity at the diagonal point 16, whereas converselyfor a 0 pulse as a polarity pulse indicating a signal of negativepolarity to be transmitted, the electronic switching element 45 isconducting so that the sampling, which is then present at the output ofthe pulse code demodulator 35, occurs with negative polarity at thediagonal point 17 and with positive polarity at the output of thediagonal point 16. In this manner the samplings of the rectified signalat the diagonal point 13 shown in the time diagram 37 are converted bythe polarity reversal arrangement into the samplings of the originalsignal which samplings are shown for the purpose of illustration in timediagrams 47, 48.

As may be evident from these time diagrams 47, 48, the samplings of theoriginal signal occur in a balanced form at the diagonal points l6, 17of the bridge, the diagonal point 17 likewise as in FIG. 1 beingconnected through an amplifier 49 having a high input resistance to auser 50, for example, a time multiplex distributor,

Finally it is to be noted that it is not necessary to make all resistor9-12 of the bridge mutually equal, but that it is already sufficient tomake the resistors 9, 10 connected to the signal source 1 and theresistors ll, 12 connected to the input of the amplifier l5 pairwiseequal.

What is claimed is I. A circuit arrangement for polarity reversal ofsignals from a signal source, which circuit arrangement is provided withtwo series-arranged electronic switching elements, characterized in thatthe polarity reversal arrangement is provided with a bridge composed ofresistors, the signal source being connected to one end of a diagonalbranch of the bridge and the input circuit of an amplifier whichreverses the polarity of the input signal being connected to the otherend of the said diagonal branch. the series arrangement of the twoelectronic switching elements being included between the ends of theother diagonal branch, the junction of the electronic switching elementsbeing connected to the output circuit of the amplifier while the outputsignals of the polarity reversal arrangement are derived from one end ofthe last-mentioned diagonal branch of the bridge.

2. A circuit arrangement as claimed in claim 1, characterized in thatoutput terminals of the signal source are connected to the said end ofthe diagonal branch and a point of fixed potential, respectively, whilein the absence of signals from the signal source both the input circuitand the output circuit of the amplifier are adjusted to the said fixedpotential.

3. A circuit arrangement as claimed in claim 1 wherein the bridge thetwo resistors connected to the signal source and the two resistorsconnected to the input of the amplifier have been made pairwise equal.

4. A circuit arrangement as claimed in claim I, wherein the amplifier isprovided with an input amplifier stage employing a field effecttransistor, the control electrode of said input amplifier stage beingconnected to the said end of the diagonal branch of the bridge and thesource electrode being connected to a succeeding amplifier stage, whilethe input amplifier stage is fed by a current source in the form of adifference amplifier employing two transistors, the base electrode ofone transistor being connected to a point of fixed potential and thebase electrode of the other transistor being connected to the output ofthe amplifier through a low-pass filter which does not pass signalfrequencies. g

5. A circuit arrangement as clalmed "'1 claim I, wherein the signalsource is formed by a current source.

6. A circuit arrangement as claimed in claim 2, wherein the electronicswitching elements are formed by diodes which, dependent on the polarityof the signals from the signal source, are brought from their blockedcondition to the conducting condition.

7. A circuit arrangement as claimed in claim 1, wherein each electronicswitching element is provided with a control electrode which are broughtto their conducting condition by control signals through control linesconnected to the control electrodes.

1. A circuit arrangement for polarity reversal of signals from a signalsource, which circuit arrangement is provided with two series-arrangedelectronic switching elements, characterized in that the polarityreversal arrangement is provided with a bridge composed of resistors,the signal source being connected to one end of a diagonal branch of thebridge and the input circuit of an amplifier which reverses the polarityof the input signal being connected to the other end of the saiddiagonal branch, the series arrangement of the two electronic switchingelements being included between the ends of the other diagonal branch,the junction of the electronic switching elements being connected to theoutput circuit of the amplifier while the output signals of the polarityreversal arrangement are derived from one end of the last-mentioneddiagonal branch of the bridge.
 2. A circuit arrangement as claimed inclaim 1, characterized in that output terminals of the signal source areconnected to the said end of the diagonal branch and a point of fixedpotential, respectively, while in the absence of signals from the signalsource both the input circuit and the output circuit of the amplifierare adjusted to the said fixed potential.
 3. A circuit arrangement asclaimed in claim 1, wherein the bridge the two resistors connected tothe signal source and the two resistors connected to the input of theamplifier have been made pairwise equal.
 4. A circuit arrangement asclaimed in claim 1, wherein the amplifier is provided with an inputamplifier stage employing a field effect transistor, the controlelectrode of said input amplifier stage being connected to the said endof the diagonal branch of the bridge and the source electrode beingconnected to a succeeding amplifier stage, while the input amplifierstage is fed by a current source in the form of a difference amplifieremploying two transistors, the base electrode of one transistor beingconnected to a point of fixed potential and the base electrode of theother transistor being connected to the output of the amplifier througha lowpass filter which does not pass signal frequencies.
 5. A circuitarrangement as claimed in claim 1, wherein the signal source is formedby a current source.
 6. A circuit arrangement as claimed in claim 2,wherein the electronic switching elements are formed by diodes which,dependent on the polarity of the signals from the signal source, arebrought from their blocked condition to the conducting condition.
 7. Acircuit arrangement as claimed in claim 1, wherein each electronicswitching element is provided with a control electrode which are broughtto their conducting condition by control signals through control linesconnected to the controL electrodes.